These are the organisms which belong to kingdom monera have cell wall made of peptidoglycan, cannot be seen with naked eye and lack membrane bound organelles. They were discovered by Leeuwenhoek. Their features resemble to the organisms of kingdom monera. Bacteria are present everywhere. The size of bacteria is not static. It is different for every species. Their size ranges from 0.1 micrometer to 750 micrometer. Bacterial cells vary in shape and they have no definite structure. They can be coccus, bacilli, spirillum, stalked in shape. Cocci bacteria are further subdivided into spherical or ovoid shape. They can occur as single, double, chain form, grape form or 3d form. Bacilli are rod shape bacteria with flat ends. Spirillum bacteria are coil shape bacteria which resemble cork-screw. Vibrio is a comma shape bacterium which causes cholera.
Flagella may or may not be present in bacteria. Bacteria they are classified according to it. They may be called Flagellate or Non Flagellate. They are further categorized depending on the location of flagella such as cephalotrichous or lophotrichous.
Bacteria are also classified on the basis of their reaction to Grams stain. They are classified as Gram positive and Gram negative. The bacteria which retain the stain are referred as a Gram Positive while their counterparts which do not retain any stain are called Gram Negative. In this bacteria are stained with alkaline solution of gentian violet .In the next step they are treated with iodine solution followed by washing with water and alcohol. Gram positive bacteria retain blue or purple color while other do not retain this color and are referred as Gram negative.
Cell envelope, cytoplasm, nucleiod, plasmids, flagella, pili, fimbrae compose bacterial cell. Cell envelope is further subdivided into glycocalyx, cell wall, plasma membrane. Glycocalyx is the mucin layer of cell envelope without cellulose. Proteins may or may not be present. A loose sheath of glycocalyx may also be present which is referred as a Slime layer. If it is rigid it is known as Capsule. It helps in the longevity of bacteria.
Cell wall provides shape and structural aspect to the cell. It lies below the glycocalyx and above plasma membrane. Cell wall is single and smooth in Gram positive bacteria. Its thickness is around 200 – 800 angstrom.
Cell wall is double layered and complex in Gram negative bacteria. Gram negative bacteria have separate membrane known as outer membrane. It consists of proteins, lipids and lipopolysachrides. The proteins present in outer cell wall are referred as porins. Peptidoglycan the main constituent of cell wall is also known as mucopeptide. Peptidoglycan is made of N- Acetyl glucosamine and muranic acid. They all are cross linked by peptide chains. An enzyme lysozyme has the ability to hydrolyze peptidoglycan. Around ¾ of cell wall in gram positive bacteria is made of peptidoglycan.
Plasma Membrane is the differential permeable membrane covering the cytoplasm. It is the innermost layer of cell envelope. It is composed of phospholipids bi layer along with extrinsic, intrinsic and Trans membrane protein. It allows ingress of nutrients and outcross of waste products.
Cytoplasm is the unstable complex which makes protoplasm. No membrane bound organelles are found. It includes mesosome, ribosome and chromatophores.
Harmful activities of bacteria
They deteriorate food stuff along with daily use house hold articles. These functions are basically performed by saprophytic bacteria. Clostridium is the most common bacteria which causes food poisoning. It affects packed food which leads to diarrhoea and vomiting. They remove important minerals from soil such as sulphur and nitrogen.
Useful activities of bacteria
They play an important role in agriculture. Their roles are similar to saprotrophic bacteria which act as a nature scavenger. Chemoautotrophic bacteria like Nitrifying, sulphur oxidizing and iron bacteria also play a vital role in agriculture. Their functions have been discussed above. Bacteria also play an important role in industries. Some of the lactic acid bacteria convert lactose to lactic acid. Lactic acid is used for multipurpose. It changes milk into cheese and yoghurt. It is used in preservation of food, preparing drugs and coagulating milk protein. There are certain bacteria which make acetic acid from ethyl alcohol and are known as Acetic acid bacteria. Some of the bacteria produce alcohol. A few of them are used to clean hides and cure tea, coffee leaves. Their major role is in production of antibiotics and vitamins mainly riboflavin and B 12.
